The treatment phase of the study will last 16 weeks. Participants will be randomly assigned to receive either 500 mg of clarithromycin or placebo twice a day, plus inhaled fluticasone. At monthly study visits, spirometry and blood collection will be performed. Standardized questionnaires to assess asthma symptoms will be completed every 2 weeks. Medical adherence will continue to be monitored. At the end of Week 16, participants will stop receiving clarithromycin or placebo, but will continue to receive fluticasone. Asthma symptoms, rescue medication usage, quality of life, and lung capacity will be assessed; tissue samples will be examined for the presence of Mycoplasma pneumoniae and Chlamydia pneumoniae. An 8-week washout period will follow to observe any lingering medication effects and to monitor for safety. Monthly study visits during this period will include spirometry and blood collection.